Dental gypsum cast

ABSTRACT

A method is disclosed for forming an accurate stone cast from a dental impression, used for the purpose of prosthetic fabrication, such as dental crowns and dentures. The initial step of this unique method is to first acquire a suitable amount of dental stone setting catalyst. One type of a suitable stone catalyst is calcium sulfate dihydrate. The dental stone catalyst is engaged onto the internal surface of the impression. This catalyst will act to hasten the initial setting of wet, mixed dental stone that is in closest proximity to the impression. The result is a stratified set of the stone. Setting of the wet, mixed dental stone occurs first at the impression/stone interface.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 11/878,337, filed Jul. 23, 2007.

In Office Action of Nov. 18, 2010, related to application Ser. No. 11/878,337, the Examiner states that changes to Claims defined in Applicant's Reply, Nov. 02, 2010, would require a further search and/or consideration.

Form SB/25 is enclosed herein in compliance with 37 CFR 1.321(c). The applicant requests the Office to accept this terminal disclaimer to overcome any actual or provisional rejection of this application based on double patenting due to any common areas of claims of patent application Ser. No. 11/878,337, entitled: METHOD AND MATERIALS TO FORM A CAST FROM GYPSUM.

The current applicant is the sole owner and, as such, has 100 percent interest in the application Ser. No. 11/878,337 as well as any subsequent patent that would arise from this application.

FIELD OF INVENTION

This invention relates generally to making better fitting dental restorations and more specifically this invention relates to making accurate stone dental casts and models, which are used in the process of fabricating removable dental appliances and indirect dental restorations.

DESCRIPTION OF PRIOR ART

Stone dental casts need be very accurate replicas of the dentition. The cast, along with other exact measurements and guidelines supplied by the dentist, enables the laboratory to make dentures, partial dentures, orthodontic appliances, bleaching trays, and nightguards.

Other special applications, such as oral snoring devices, obturators, and surgical stents, may also be prescribed by the dentist.

Once a cast is made, it can be sectioned so that segments can be removed. Segments representing individual teeth are referred to as dies. The dies are indexed in various ways to give an accurate and reliable placement of the removable die in and out of the model base. Some practitioners will refer to this dental cast with removable dies as a dental model. And they will refer to the one piece stone pour of the impression as a dental cast. However, many practitioners will still use the term “cast” and “model” interchangeably and do not distinguish between the two terms.

Dental models are used in the dental laboratory to create dental restorations which ultimately will be delivered to the dentist office. These restorations are then cemented into the patient's tooth with a cement, such as zinc phosphate cement. These cemented restorations are referred to as indirect restorations. Examples of indirect restorations would include inlays, onlays, veneers and crowns.

When initiating an indirect restoration for a patient, the dentist will first carve the tooth structure into a certain shape. This finished carved tooth is referred to as a prepped tooth, or simply, the preparation. After this step of tooth preparation is accomplished, impressions are taken to record the new altered dimensions, that is, a moldable material is impressed upon the tooth and allowed to set. Elastomeric materials are sometimes employed for this. Examples of elastomeric impression materials would include polyvinylsiloxane, polyether, and rubber base.

Collectively, all of the impression materials cure to the shape of the teeth and mouth. The impression material is removed from the mouth, capturing a negative image of the impressed area of the oral cavity.

In the lab, a wet mix of stone is poured into the impression. Upon hardening, after an hour or so, the resultant dental cast is separated from the impression. This cast will be used as a die in the process of fabricating removable appliances, such as dentures and the like.

The fabricated dentures are delivered to the patient by the dentist. Any irregularities in the fit of the appliance are located and adjusted by the dentist. A similar process takes place for all removable dental appliances.

So the process of taking impressions avail the patient dentures and cast crowns. These products would be very challenging to make without an indirect technique.

Crowns are also delivered from the dental laboratory to the dentist office. These restorations are then modified and cemented for the patient by the practitioner.

However, as beneficial impression dentistry has proven to be, a tremendous problem still exists with indirect dentistry. Dental appliances and indirect restorations seldom have a perfect fit. All mouth appliances, such as dentures, and all tooth restorations, such as crowns, need varying amounts of chair time to adjust. Distortions must be compensated for before finalizing the products.

Similar to the irregularities associated with dentures, acrylic nightguards also usually end up with a compromised outcome. Indeed, dentures do require multiple appointments to finalize. And usually, the final outcome is a slight disappointment. Dentures are usually tolerated by the wearer; dentures are seldom as tight fitting as the dentist would prefer. Nightguards share the same fit problems as dentures. It is very time consuming to troubleshoot an ill-fitting nightguard. In fact, many dentists have resorted to a soft inside liner attached to the hard outside acrylic shell. This laminate design is not so much for patient comfort, but for ease of delivery. The soft material is very moldable and therefore does not have to be a precise fit to the dentition. Its inherent conforming shape compensates for fabrication irregularities. However, the soft liner is not as durable and long lasting as all hard acrylic.

The Applicant has recently attended the 2010 Greater NY Dental. On Nov. 27, 2010, Drs. DiLauri and Browne, associated with the Pankey Institute in Florida, spoke of occlusal concepts.

Much of therapy for occlusal problems relies on acrylic appliances that are made using impressions and stone casts. When questioned on how they adjust the internal fit of the appliance to the mouth, both DiLauri and Browne acknowledged that they perform a reline of the new appliance. The Applicant could only assume a relining is necessary due to the poor fit of appliance. Even experts in our field, such as DiLauri and Browne, are challenged by impression dentistry.

Dr. Terry Tanaka, D.D.S. has published numerous articles and is widely recognized as a research anatomist and for his teaching of advanced restorative procedures. On Nov. 28, 2010, Dr. Tanaka also spoke in New York on occlusal concepts. Dr. Tanaka is expert at making removable appliances. He also stated that he took new finished appliances and refined them by a self cure acrylic resin.

SUMMARY OF THE INVENTION

Acquisition of powdered calcium sulfate dihydrate, or adequate stone setting catalyst substitute, is the initial step. This inventor produced the catalyst, calcium sulfate dihydrate, by mixing dental stone with water and allowing full set. The resultant set dihydrate stone is then ground into a powder with a fine acrylic adjusting bur.

An elastomeric dental impression is procured in a manner familiar to the dentist. This inventor has found no specific correlation to any specific type of impression material, or to any specific style of tray design, that effects final outcome.

This set impression is placed aside for use in the dental lab.

Calcium sulfate dihydrate powder, or a stone setting catalyst substitute, is shaken lightly onto all of the internal surfaces of areas of interest of the dental impression. This powder is then burnished with a suitably stiff artist brush onto the impression surface. Excess loose powdered calcium sulfate dihydrate is blown away, leaving a light dusting held in intimate contact to the surface of the impression.

Last, the dental impression is poured with wet, mixed dental stone.

DETAILS OF THE PREFERRED EMBODIMENT

The steps outlined of adding catalyst to the surface of the impression has the function of causing a chemical reaction. This chemical reaction is exhibited as the wet stone in close proximity of the impression surface begins to set, sooner than usual.

The mixed stone closest to the catalyst sets sooner, as compared to that portion of stone, from this same initial stone pour, located further away from the impression/stone interface, and further away from said placed catalyst on the impression surface. The Inventor refers to this setting phenomenon, as a “stratified” set of stone.

The theory of operation is that the poured wet stone closest to the impression will set faster, due to the presence of a stone setting catalyst. The rest of the mix of the stone pour will set slower. The presence of a catalyst will, thus, cause the first pour of wet mixed stone added to the elastomeric dental impression to set in a stratified fashion.

The novel placement of a surface catalyst will ultimately cause a cast to form, possessing unique dimensions. The presence of a catalytic means to initiate the set in a strategic area will create an effect, causing a unique change in the way the stone sets. Thus, the stone accuracy will not be adversely affected by setting distortion, which still does occurs, but in the peripheral areas.

Distortion is directed to other areas of the cast that are away, and removed from, the important target areas of the cast at the stone/impression interface. This guided setting of stone will result in the formation of a more accurate cast.

OBJECTS AND ADVANTAGES

The fact that experts give varying reasons for the problems associated with impressions proves, most importantly, that the problems really do exist. This reality of ill-fitting restorations is best summarized by Sharp, et al. in U.S. Pat. No. 5,911,580. In column 1, they describe the normal process of a dentist usually having to adjust an appliance. They write of the possibility that the final outcome may be that the appliance could not be adjusted adequately. The appliance sometimes needs to be remade.

Prior art shows that there have been many attempts to identify the cause of ill-fitting crowns. In U.S. Pat. Nos., 6,045,359, 5,478,235, and 7,021,929 inventors modify dental impression tray designs. They hope to achieve better bonding between the impression material and the tray. Although it is true, that a bond is needed between the impression material and the tray, any severe defect such as tray separation would create a gross discrepancy in fit of final appliance. These separations are usually evident to the practitioner at the time of tray removal from the oral cavity. Impression tray design alone has never made a further refinement in the fit of our dental castings.

Inventors of prior art have attempted to create new impression materials to increase accuracy. In U.S. Pat. Nos. 6,861,457 and 5,907,002 Kamohara recognizes the inaccuracies associated with polyether impression material. He further isolates the problems of inaccuracy to impression tray removal. He feels that recovery from deformation, due to forces applied at the time of impression removal, causes dimensional instability. He feels the solution for ill-fitting crowns is use of a more accurate impression material, with a more resilient design. With all of the impression materials on the market today, including the new ones introduced by Kamohara, there is very little improvement in the reliability of indirect dentistry.

Some inventors believe the inaccuracies occur after the impression is completed. They feel distortion occurs during the modeling process. This is the case with inventor Singer in U.S. Pat. No. 6,149,426. He states that inaccuracies occur with the master cast. His prior art confirms that the prosthetic must be fitted and corrected several times before it becomes accurate. He further feels that the problem, however, exists in the plastic trays used in the profession as well as subsequent modeling of the impression. His invention does not yield a better fitting crown.

Some practitioners believe that prior art, specifically Eisner (U.S. Pat. No. 4,243,389), and Shilliday (U.S. Pat. No. 3,650,031) already places a thin layer of wet stone into the impression. However, the Applicant disagrees. In the drawings for the Eisner patent, the entire tooth portion of the impression must be filled to support the placement of a dowel pin. This is not a thin layer of stone.

The same is also true with Shilliday, who also fills most of the impression with stone on the first pour. Neither Eisner, Shilliday, or any prior art, first places a thin layer of dental stone. Therefore, specifically, they do not first place a thin layer of catalyst to the impression surface.

Additionally, Eisner does not first place a catalyst before his first pour of stone. Eisner places wet mixed stone, not a thin layer, but, conversely, enough to fill at least the tooth portion of the impression.

Eisner's first pour of wet stone will therefore have no benefit of a strategically placed catalyst. Eisner's first pour will set in the normal fashion of present day art. It will distort because most, if not, all, of the tooth portion of the impression is filled with wet stone. Prior art does not place a catalyst to influence the setting of dental stone deposited into the dental impression.

Only a thin deposition of wet stone would leave a residue, sufficiently light, or thin, of catalyst, when set. Eisner does not place such a thin mix of stone. In contrast to the Applicant's disclosure, Eisner sufficiently fills his impression, as in all prior art, and this allows for setting stone distortion, unknowing to the practitioner. His cast is not accurate.

Again, wet stone, poured with Eisner's recipe does not possess the working properties of a catalyst and is ineffective in forming a cast of unique dimensions.

No operative exists from Eisner to form a more accurate cast. His invention is only exemplary of current methods of pouring dental impressions. By not recognizing the need of first placing a stone setting catalyst, his style of pouring indexed dies will be no more accurate than present art.

The novel invention described herein, has the first pour of stone configured to rest against catalyst, so that the first pour of stone is designed to set in a special way. This is unique. The specific portion of wet stone nearest the impression, and, thus, catalyst, will begin to set sooner, compared to other areas of the same wet stone mix, located away from the catalyst. This represents a stratified set of wet stone within the one pour of wet mixed stone.

In the Applicant's invention, initial setting of the first pour of stone occurs along the impression/stone interface, while residual setting within this same said first pour of stone, occurs later, and away from the impression/stone interface. Therefore, accuracy along the impression/stone interface is captured. Distortion caused by setting stone occurs innocently, away from the impression surface. The inventor calls this a stratified set. The Applicant's use of term “stratified” set is just a generic way of stating that setting occurs differently within the first pour. Setting is NOT now a single event throughout the entire mass. A single event setting would cause distortion throughout the stone cast, including the surface area duplicating the oral structure.

Pouring of stone in multiple layers is common in the profession.

The strata is of the present disclosure is different and unrelated to the customary strata recognized in our present day use of layering different pours of stone to form a desired configuration for mounting of stone casts.

The pouring of stone in layers is common and is core to present day technology. Layering of stone is carried out in virtually all of impression dentistry. This is exemplified by Shilliday, Eisner, and Jinoian. All of these inventors place an initial pour of stone, and, later, apply a second pour, applied to the first pour.

This age old formula for pouring casts has only lead to ill-fitting appliances and most not be confused with the improvement of the new invention described at length.

In the instance of prior art, as exemplified by Eisner, a certain amount of stone is poured into the impression and then allowed to set. Afterward, an additional pour of stone is made onto the first pour, and now, the second layer is allowed to set. This process can be repeated many times. The resultant mass of dental stone would be “stratified”.

The layering or “strata”, of this invention, occurs within the first pour of stone (not within layers and layers of additional pours of stone). NO other prior art teaches a stratified set within this first pour of stone. Even though the layering still involves dental stone in both cases, the dissimilarities are significant.

A mounted cast may therefore have stone strata made from the different pours (layers), all the while, having strata (setting) within just the first poured layer. Here, the two types of strata exist in the same cast and, yet, be identified with different structure and function. Again, ALL prior art first places some amount of wet mixed gypsum. However, first pours are never in the form of a very thin layer to act as a stone setting catalyst. Every stone cast ever made was by pouring some varying amounts of wet mixed stone into the dental impression.

In the broadest interpretation, most casts are stratified or layered, but, this is only due to mounting configurations. In these instances, the term, stratified, only pertains to added layers of stone over the initially poured set layer of stone. This is a stratified pouring of stone. It does not represent a stratified setting of stone. The guided setting of stone, is this accurate way, is unique to this application. It is, thus, unobvious.

Therefore, pouring stone in multiple layers, may also be deemed “stratified”, but is, however, unrelated in form and function to the current invention.

However, in no case in prior art is the first single pour of stone made to set in a stratified manner. Nowhere is our prior art, in practice or research literature, references first placing a thin layer of stone setting catalyst onto the elastomeric impression surface.

No operative exists to influence the setting of the first layer of wet mixed stone.

The present disclosure pours the first mass of mixed wet stone against a catalyst that is present on all of the important internal areas of the impression. This first mass is one pour. And this first pour will be enough to at least cover all of these important target areas of the impression.

The stratified setting occurs within this first pour of stone. This resultant cast, when the wet stone has set, will be accurate.

The present disclosure is unique by first placing a thin layer of gypsum, or catalyst. This thin initial placement affects outcome. Thin placement of gypsum is not recorded anywhere in our dental literature. This supports unobviousness.

Eisner's patent does not mention accuracy. Speaking with him directly, he states that his sole purpose of this invention was exclusively to form a model having parallel dowel pins.

He states that he was not trying to improve accuracy. Eisner volunteered a testimonial letter.

The Applicant discloses herein how his novel technique defines a difference in final outcome of accuracy. The physical unique gypsum structure, made from a stratified setting of stone, serves a function of creating the impression surface of the cast that more accurately duplicates oral structure.

Some dental professionals feel that casts are already completely accurate. The reality is, that professionals strive for accuracy. No one claims complete accuracy.

If, by chance, accurate casts are ever mentioned in the literature, it means that the accuracy is not ill-affected; that the cast accuracy is not affected by the particular process of the discussion in that article.

An example would be Eisner. Eisner invents a dowel pin setting device. He has in essence changed the pouring process of a dental gypsum. He is able to perform this with apparently no added distortion to the cast. There are no adverse affects. Therefore, he, or like many other pioneers, may state that the casts are accurate.

What the inventors or authors are really stating, is that their new configurations of the gypsum casts are more convenient in use and, all the while, accuracy is not sacrificed; their new configurations are not detrimental to accuracy. I belief that most of the dental professionals would understand this use of the word “accurate”, as its use is rather common in our publications. Researchers are not implying complete accuracy, and this is understood.

So, admittedly, the term accuracy does creep up in the literature, but it is understood by the profession in its implied context. Again, in professional circles, “accurate” would really mean “unaffected accuracy”.

Stone manufacturers publish tables for setting expansion of their gypsum products. If the stone manufacturers admit distortion, and even quantify it, then it would be difficult for dentists, using this same gypsum, to defy science and create their own tables of 0% distortion. Dentists, using this same gypsum, cannot claim complete accuracy.

Due to setting stone distortion, casts are not completely accurate. Room for improvement always exists.

Tests are designed to assess stone setting expansion. Manufactures pour wet mixed stone into a standardized mold. Measurements are taken as the setting stone distorts. Such a device was personally demonstrated directly to the Applicant at WhipMix Corporation in Louisville, Ky., May, 2009.

Dentists don't necessarily pour stone into standardized molds, but will pour wet mixed stone into impressions. These impressions are certainly not standardized, however, the stone will still distort the same quantitative amount, as if poured into a standardized mold. Setting of stone expansion tables prove inaccuracy exists with current day casts. Eisner's models distort. He will fill the entire tooth portion of the impression with a single pour of stone. The manufacturer's tables will show the data as far as how much Eisner's model would be expected to distort.

This inventor uses the same gypsum products as does Eisner, Shilliday, and prior art. The Applicant's casts will also distort, volumetrically, and to the same proportional degree as in present and prior art. However, the stone is directed to set in a certain unique fashion. Due to the placement of a thin coating of catalyst to the impression surface, setting of stone first occurs along the impression surface. This is where accuracy is needed. Instead of distortion affecting the entire cast as a whole, distortion will now occur in areas of mixed stone further removed from the impression surface.

The stone will first set along the impression surface and later in the peripheral areas. (stratified setting of stone).

Aside from the evidence shared, it must be remembered that the progression of events causing stated better results are logical and intuitive. Although never carried out before, it would be reasonable to assume that a mechanism to cause the stone to set first at the impression level could possibly result in improvement.

No inventor has ever added a THIN layer, or dusting, of stone, or catalyst, to the impression surface. The referenced Eisner patent shows the addition of the first pour of stone (catalyst) to effectively fill most of the tooth portion of the impression. This is not a thin layer of stone. It is exemplary of common place handling of dental impressions. The inventor himself has done the same for thirty years. Casts made in such fashion suffer from the inherent distortion properties of setting stone.

Shilliday also pours his first layer of stone, again, effectively filling the impression, with no thin layer of stone catalyst present. Shilliday effectively fills most of the dental impression. No initial thin layer exists.

The results of the Applicant's invention may be seen on YouTube. Search “Dr. White NTI” for location or direct to www.youtube.com/watch?v=vCbcCFEESK4. The Applicant does not have to reline his appliances, while the most noted speakers in the country, do. The significance cannot be overstated. Those with extraordinary skill in the art are not aware of the disclosed novelty. Obviousness cannot be a basis for rejection.

Also enclosed is a copy of testimonial letter written by Dr. Steve Harris. Dr. Harris is the only dentist instructed on use of using a stone setting catalyst as described in this disclosure. He has thirty years of experience and recognizes a distinct difference using a stone catalyst.

CONCLUSIONS, RAMIFICATIONS AND SCOPE OF INVENTION

To utilize this invented technique, acquisition of powdered dental stone is achieved and this can be accomplished by most technicians. The powdered catalyst can be stored for later use. A small portion of powdered catalyst can serve for many impression pours. The dental stone manufacturers could supplement their current products with a separate inclusion of dental stone catalyst. This packaging from the manufacturer would be more efficient, saving the dentist or technician the time and effort of producing their own powdered catalyst.

Hopefully, a generic catalyst would be produced that would not be stone type specific. This catalyst could be made available for use that would be compatible with all dental stones. This inventor has not yet studied all the various combinations of catalysts used with different brand and type dental stones.

In addition to the powdered form of catalyst described above, dental stone catalyst could be made available in a liquid slurry form. Such a liquid product would allow for a dipping of the impression. The liquid will evaporate, only to leave a thin precipitate film coating on the impression material to act as a dental stone catalyst.

Other ways may exist to attach the catalyst to the impression surface. One ramification would be simply to discard an initial stone cast and repour the impression with a subsequent pour of stone.

By pouring the stone cast first, and then removing the resultant set cast, a fine residue remains of the set stone onto the impression surface. Unobvious to even those expert in the art, the second cast retrieved from the impression will be dimensionally different from the first cast; it will be a more accurate cast than the first cast.

Removing the first cast will leave a set stone residue, enough to act as an effective catalyst. This is another mechanism for attaching the stone setting catalyst.

That is, the dental impression is first poured in the usual manner with gypsum. After the stone mix is set, the resultant cast is removed.

Some very small amount of the first pour of stone remains attached to the impression surface. This is in the form of set gypsum, which is a good stone setting catalyst.

When a second pour of stone is now added to the impression, catalytic means is present to functionally influence the setting of stone. The stone will now set in a stratified manner due to the presence of the catalyst. That portion of the second pour of stone, closest to the impression surface, will set faster, while portions of the same stone mix, located further from the impression surface, will set later.

The catalyst may also be applied to the impression surface as a wet stone mix. Wet mixed dental stone could be applied directly to the dental impression. The technician would vibrate a portion of wet mixed stone into the impression, then, directly and immediately, invert the impression and vibrate to expel all but a very thin layer of wet stone. Most of the wet stone would be released from the impression, leaving only a thin coating, certainly less than 10% of the space represented by the tooth portion of the dental impression. Catalyst would thus cover the internal surface of the impression. With the right conditions for success, allowing such a thin coating to set, before addition of more wet stone, would be one way to effectively add catalyst to influence cast accuracy. It would be tantamount to adding a thin layer of catalyst.

This very thin layer would cure to produce a direct deposit of dihydrate calcium sulphate. This thin application will itself be a layer of catalyst after it is given sufficient time to cure. Subsequent addition of more dental stone will finalize the impression pour.

The Applicant explains how to form this unique gypsum cast structure and how the resultant cast accuracy is different from present day. The inventor further reiterates the difference between a stratified setting of stone, versus a stratified layering of stone.

The Applicant discloses how his novel technique defines a difference in final outcome of accuracy. The physical unique gypsum structure, made from a stratified setting of stone, serves a function of creating the impression surface of the cast that more accurately duplicates oral structure.

The layering of stone is common and is core to present day technology. Layering of stone is carried out in virtually all of impression dentistry. This is exemplified by Shilliday, Eisner, and Jinoian. All of these inventors place an initial pour of stone, and, later, apply a second pour, applied to the first pour. However, in all cases, the initial pour is not a thin pour. As such, even though the initial pour creates a stone setting catalyst when cured, it is ineffective in directing the outcome of accuracy. Prior art will pour a sufficient amount of stone that will set spontaneously and distort within itself. It is poured without the guidance of a catalyst. And once a dental cast is inherently distorted, it would not be able to serve as a foundation for a final product that is expected to be accurate. The damage is irreversible. This age old formula for pouring casts, with a heavy first deposition of wet stone, has only lead to ill-fitting appliances and most not be confused with the improvement of the new invention described at length.

The Applicant discloses, not layering of stone in strata, but setting of stone in strata. Implementation of this discovered technique enables dental impressions to yield more accurate casts than present day technology.

This distinctive invention advances dental restorations beyond present art and this invention improves the overall standard of care.

Accuracy, to this level, has never been appreciated in dentistry. This disclosed technique will add normalcy and stability to a process that, heretofore, is far from predictable. This new technique is the answer to what may be the last major challenge in our profession.

To be able to significantly reduce procedural office time is not to be understated. This technique will not only cut delivery time for the dentist, it produces a better product. Patients will enjoy restorations that will feel better and last longer. This unique disclosure is long overdue. The profession has accepted status quo level of accuracy in dentistry for a very long time.

The Applicant does not specific a particular type of catalyst. No inventor has ever added stone setting catalyst to cause a stratified set of stone to form a more accurate cast. Therefore, placement of any catalyst describes novelty. Naming a specific type of catalyst, as this Applicant has invented, to assure accurate casts, should not be a requirement for novelty. 

1. An improved method for producing a stone dental cast comprising the steps of: a. placing a thin layer of dental stone setting catalyst, onto the internal surface of an elastomeric dental impression; b. pouring a wet, mixed dental stone into said elastomeric dental impression and onto said catalyst, whereby the dental stone juxtaposed to said catalyst sets faster, and further whereby, an accurate gypsum cast is formed by a stratified set, thereby, producing accurate restoration or prosthesis.
 2. A method according to claim 1, wherein said dental stone setting catalyst comprises dental stone remnant attached to said internal surface, from a previous stone pour.
 3. A method according to claim 1, wherein said dental stone setting catalyst is a thin layer of wet mixed dental stone.
 4. An improved method for producing a dental stone cast comprising the steps of: a. placing a thin wet, mixed dental stone layer onto elastomeric impression surface, b. allowing cure of said mixed dental stone layer, then c. pouring sufficiently more wet, mixed stone into elastomeric impression and over said dental stone layer to make a dental cast.
 5. A method for making a dental gypsum cast comprising the steps of (a) pouring wet mixed dental stone into a dental impression of oral structure, wherein said dental impression comprises cured elastomeric material (b) setting of said wet mixed dental stone (c) recovering cured dental stone from said cured elastomeric material, the improvement comprising control of stone setting deformation by fixing thin layer of stone setting catalyst onto all internal surface areas of interest of said cured elastomeric material.
 6. Said stone setting catalyst, of claim 5, is thin layer of residual stone from previous stone pour. 